Electrical submersible pumps (ESP) are commonly used to pump oil and water from hydrocarbon wells. A typical ESP has a pump coupled to a motor and driven by a shaft rotated by the motor. The pump, which is often a centrifugal pump with a large number of stages, creates down thrust on the shaft. The ESP has a thrust bearing to transfer down thrust on the shaft to the housing. The thrust bearing includes a thrust runner rigidly mounted to the shaft and a thrust pad or base that is rotationally engaged by the thrust runner. The thrust pad receives thrust from the thrust runner and transfers the thrust to a housing of the ESP.
In some instances, the thrust can be very large. Because the diameter of the ESP is restricted, tandem thrust bearings may be employed to accommodate larger thrust. Tandem thrust bearings include upper and lower thrust runners rigidly mounted to the shaft. The upper thrust runner transfers a portion of the thrust from the shaft to an upper bearing pad. The lower thrust runner transfers another portion of the thrust from the shaft to a lower bearing pad.
One difficulty occurs in sharing the amount of thrust transferred by the upper and lower thrust runners. Because of tolerances and thermal growth of the shaft relative to the housing, it is difficult to achieve a desired amount of load sharing. Various proposals have been made to share the load between tandem thrust bearings.